Normally, the shifting of ratios in a transmission system is effected by a shift finger acting on a set of transmission forks in the transmission. The shift finger is acted on by a shift lever extending outside the transmission and supported in a supporting mechanism.
Conventionally, on a rear driven vehicle, the shift lever is directly operable on the transmission system and is mounted in a housing extending from the top thereof. On a forward driven vehicle, the shift lever is normally remotely operable on the transmission system by means of a remote control shift assembly. The remote control shift assembly normally comprises a series of levers, or other means such as, for example, cables or hydraulic mechanisms, to which the shift lever is connected.
Known shift lever supporting mechanisms comprise an enlarged spherical portion disposed on the shift lever. The spherical portion is arranged in the mechanism in a retaining cup and is operable, through sphere-to-sphere engagement, to pivot therein to perform shifting operations. The retaining cup is housed in a housing through which the lever extends.
Shift lever mechanisms also generally comprise biasing means operable to provide a biasing force on the lever when it is shifted from a predetermined neutral position.
Known biasing means generally comprise a pair of diametrically opposing return pins operable to contact opposite side surfaces of the lever. The return pins are disposed along an axis transverse to that of the lever in a biased neutral position and are operable to apply a biasing force on the lower regions of the side surfaces of the lever. A gap, due to manufacturing tolerances, normally exists between each side surface and the associated return pin.
In use, pivotal displacement of the lever, from a neutral position, causes it to abut the relevant return pin and, on further displacement of the lever, displaces the return pin against the biasing force of a spring, thereby applying a returning force on the lever operable to encourage the lever back into the neutral position.
Means operable to provide resistance to displacement of the lever into a predetermined position is usually in the form of a biased detent pin, disposed in a transverse direction relative to the return pin, and adapted to provide resistance to displacement thereof. Because the resistance is provided relatively remote from the user, that is, at a distal end of the lever, and through biasing means, the user experiences undesirable distant and non-responsive feel in the shifting action. Further, because of the relative remoteness of the detent from the user a relatively large spherical portion is required to provide sufficient leverage on the return pin to overcome the resistance provided by the detent pin. Furthermore the resistance is only applicable on the lever in a direction in which a return pin is disposed.
Means operable to indicate disposal of the lever in one or more predetermined positions are usually suitably disposed to be actuated by the return pin or the detent pin. Again this is undesirable because of the above mentioned disadvantages.
The abovementioned known mechanisms experience undesirable movement of the lever due to biasing means, in the form of return pins, being disposed only in limited directional positions relative to displacement of the lever. In order to have a completely biased lever it would be necessary to have a return pin disposed in each direction in which the lever is displaceable. This would clearly be uneconomic as each return pin requires a hole machined into the housing in which it is disposed.
Further, the gap between each side surface of the lever and the associated return pin translates into undesirable movement of the lever, which is felt by a user.
Furthermore, the disposition of the return pins, transverse to the longitudinal axis of the housing, and the length of travel required in the pins to provide the desired biasing force, dictates the overall minimum width of the mechanism.
It is desirable for the user to experience a positive feel and positional certainty when the lever is displaced into predetermined positions, including neutral positions.
Further, it is desirable to increase the functional efficiency of shift lever mechanisms and to reduce costs related to manufacturing thereof.
Furthermore, a compact mechanism, the size of which is not dictated by elements thereof extending radially outwards from the longitudinal axis of the housing, is desirable.